1. Field of the Invention
The present invention relates to a multiscrew extruder device for production of elastomeric compounds.
In particular, the invention pertains to a multiscrew extruder device for production of elastomeric compounds intended for manufacturing tyres for vehicle wheels.
2. Description of the Related Art
A tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply having respectively opposite end flaps in engagement with respective annular anchoring structures, integrated into the regions usually identified as “beads”.
Associated with the carcass structure is a belt structure comprising one or more belt layers, disposed in radially superposed relationship with respect to each other and to the carcass ply and having textile or metallic reinforcing cords with a crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre.
A tread band of an elastomeric compound, like other semifinished products of the tyre, is applied to the belt structure, at a radially external position. The tread band can be produced by extrusion. Through extrusion a semifinished product is obtained which is defined by a band or strip having a predetermined profile in cross-section, said band being devoid of the tread pattern and being cut to size based on the sizes of the tyre to be made.
Respective sidewalls of an elastomeric compound are also applied, at an axially external position, to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads, which sidewalls too can be manufactured beforehand in the form of extruded or drawn section members.
Subsequent to building of the green tyre carried out through assembly of respective semifinished products, a vulcanisation and moulding treatment is generally carried out which aims at determining structural stabilisation of the tyre through cross-linking of the elastomeric compounds and at impressing the tread band wound around the carcass before vulcanisation with a desired thread pattern, and the sidewalls with possible distinctive graphic marks.
Preparation of the elastomeric compounds required for manufacture of the above mentioned components is known to take place by means of continuous-working extruders.
For instance, document US 2004/0094862 A1 discloses a multishaft extruder adapted to prepare an elastomer containing a filler and further additives. The extruder comprises the following regions: a feeding region at which the elastomer and additives are measured, a plasticization region provided with at least one element suitable for mixing, where the elastomer and additives are transformed into a mixture, a region provided with another element suitable for mixing, in which the filler is ground and distributed in the elastomer. The extruder comprises an outer housing accommodating an inner core and between which a chamber is defined which houses extrusion screws. The extruder has a cooling system for the inner core and a cooling system for the outer housing.
Document US 2007/0121421 A1 disclosed a multishaft extruder comprising a housing and an axial core. Defined between the housing and axial core is a circular chamber housing a plurality of parallel shafts. The core has an axial hole and an outer spiral channel which are adapted to be passed through by a cooling liquid.
The housing comprises a plurality of annular segments provided with holes for a cooling liquid. Each of the segments further has electric heating means disposed on an outer circumference thereof.